1. Field of the Invention
The present invention relates generally to workpiece handling devices and, more particularly, to a vacuum operated chuck for securing a substrate to a substrate handling device in processing systems.
2. Background of the Related Art
Modern semiconductor processing systems include workpiece handling devices such as wafer indexing devices, wafer pre-alignment devices, wafer transfer robots, and the like to handle and manipulate various workpieces such as processed and/or unprocessed silicon wafers during the fabrication of semiconductor devices. The various workpiece handling devices may be employed within a variety of operating environments having different environmental characteristics. Certain processing steps may require, for example, that the wafer be handled within process chambers such as degas chambers, substrate preconditioning chambers, cooldown chambers, transfer chambers, chemical vapor deposition chambers, physical vapor deposition chambers and etch chambers. The operating environments within these process chambers are typically high-vacuum environments and may include various combinations of high temperature operating conditions, energized gas plasma fields, and/or damaging chemical agents introduced therein while the wafer is being handled within the process chambers.
It is generally desirable that the wafer or other workpiece being handled be securely held to the workpiece handling device within the various operating environments. FIG. 1 shows a prior workpiece handling chuck 1 previously utilized to secure a wafer to a wafer pre-aligner. The pre-aligner chuck 1 includes a large vacuum chuck area 2 having a series of intersecting radial and circular grooves 3, 4. The chuck 1 shown in FIG. 1 contacts a wafer over substantially the entire surface of the chuck. Because of its large vacuum chuck area 2, this type of chuck can exert high stress forces on the wafer, particularly if the wafer is warped and the chucking forces acting on the wafer force the wafer into a into a planar orientation. In addition, the large vacuum chuck area 2 between the chuck and the wafer can produce an undesirable number of particles within the particular operating environment due to sliding contact between the back-side of the wafer and the chuck. Further, this type of chuck is typically constructed of aluminum. The undesirable metallic contact with the back-side of the wafer being handled can damage the wafer during handling.
To partially address the problems created by prior workpiece handling devices such as the chuck 1 shown in FIG. 1, other prior workpiece handling devices such as the chuck 5 shown in FIG. 2 utilize resilient members 6 disposed in one or more grooves 7 within the chuck 5 for reducing initial surface contact between the metallic chuck body 8 and the wafer 9. However, it has been found that such chuck designs do not sufficiently reduce the surface contact between the wafer and the chuck body during and after vacuum sealing has been effected. It has also been found that such chuck designs do not sufficiently reduce the high stress forces exerted against the surface of even marginally non-planar substrates by the vacuum pressure sealing forces which are still exerted against substantially the entire back-side surface of the wafer being handled. In addition, the inclusion of resilient members into the often harsh operating environments may present process complications as the resilient materials are exposed to processing conditions within the operating environments that may be incompatible with resilient materials. Such incompatibility may create undesired particles within the operating environment due to decomposition or other destructive effects acting on the resilient member.
Other prior systems have attempted to solve the aforementioned problems associated with chuck designs. FIG. 3 shows a third type of prior workpiece handling device 11, which attempts to reduce the surface area of the chuck in contact with the wafer by providing one or more vacuum chuck projections 12 mounted to the sealing surface of the chuck body 13 to minimize the contacting surface area between the chuck 11 and the wafer 9 or other workpiece being handled. However, these prior chucks still utilize resilient sealing members associated with each of the projections, which as described above, may not be desirable in certain operating environments. Over time, these resilient members must be replaced and may cause contamination during use.
Accordingly, there is a need for a workpiece handling device and, more particularly, a wafer handling chuck having a reduced contact surface area between the wafer and the chuck sealing surface, and having no resilient members associated therewith exposed to the operating environment in which the wafer is to be handled.